In many types of electronic devices, such as portable and laptop computing devices, video recording devices, servers, and so on, an electric motor may be used to drive a cooling fan to dissipate excess heat generated within the device. By removing excess heat, processors and other components of the device can operate reliably and over extended periods of time. When excess heat is not removed, electronic devices can fail, often with serious consequences, such as loss of data, loss of processing resources, or total system failure.
When using an electric motor to drive a cooling fan, especially in portable electronic device applications, a premium may be placed on the power efficiency of the electric motor. Thus, fans driven by motors that consume an inordinate amount of battery power may not be best suited for use in portable devices. In applications such as laptop and desktop computer environments in which users may be located in close proximity with the device, electric motor-driven cooling fans may emit an unacceptable level of acoustic noise that may be distracting to the user.
To bring about the efficient and quiet operation of an electric motor, one or more of the motor's operating parameters may be monitored. In some types of electric motors, a Hall-effect sensor has been used to determine an angular displacement of a rotor within the electric motor to ensure that excitation voltages used in driving the motor are selected with appropriate precision. However, the use of such Hall-effect sensors may increase the cost of electric motors and may also be subject to misalignment and failure.